Madonna has condemned the two-year jail sentence given to three members of the Russian band Pussy Riot, describing the conviction as "inhumane".

On Friday, Maria Alyokhina, Nadezhda Tolokonnikova and Yekaterina Samutsevich were found guilty of hooliganism motivated by religious hatred, receiving a two-year prison sentence. The women had been charged in connection with an anti-Putin "punk prayer", performed inside Moscow's Cathedral of Christ the Saviour in February. As Madonna pointed out, the protest lasted only 40 seconds – although it has since been viewed by millions online.

"Even if one disagrees with the location or how they chose to express themselves, the sentence is too harsh and in fact is inhumane," Madonna wrote on Facebook. "I call on all those who love freedom to condemn this unjust punishment. I urge artists around the world to speak up in protest against this travesty. They've spent enough time in jail. I call on ALL of Russia to let Pussy Riot go free."

Alyokhina, Tolokonnikova and Samutsevich had already been held for more than five months, without trial, by the time Madonna first voiced her support. At the beginning of August, when artists such as Faith No More, Red Hot Chili Peppers, Pete Townshend, Franz Ferdinand, Sting and Jarvis Cocker had condemned the women's arrest, Madonna's only comment on the matter, to a Russian television network, was that she was "sorry that they've been arrested". That changed when the singer prepared to play a stadium gig in Moscow, first by asking for the judge's leniency and then by appearing on stage in a balaclava with the band's name stenciled on her back.

Putin supporters responded with disapproval: deputy prime minister Dmitry Rogozin suggested Madonna was a "slut … lecturing everyone on morality". But the singer seemed emboldened: at an appearance in Kiev she spoke out in favour of Yulia Tymoshenko, Ukraine's jailed former prime minister, advising the crowd to "fight for what is right". She also advocated against anti-gay legislation in St Petersburg, referring to a new law as a "ridiculous atrocity". Ten anti-gay activists are now suing Madonna, demanding $10m for "moral damages and suffering".